ONPG BROTH

ONPG (Ortho-nitrophenyl beta-D-galactopyranoside) is a synthetic colourless compound (galactoside) structurally similar to lactose. ?-galactosidase positive organisms cleave ONPG to galactose and o-nitrophenyl, a yellow compound. The ONPG test is especially useful in the rapid identification of cryptic lactose fermenters (late fermenters). Since members of family Enterobacteriaceae are routinely grouped according to their lactose fermenting ability the ONPG test is significant here. ONPG Broth is used to differentiation of organisms based on their ability to utilize Ortho-nitrophenyl beta-D galactopyranoside. ONPG is similar in structure to lactose. The presence of two enzymes is required to demonstrate lactose fermentation in a conventional test.

for the di?erentiation of microorganisms on the basis of beta-galactosidase activity